Patent GB-621575-A (GB)
Title: Combined radio direction and distance finding system
IPC: G01S13/84
Filed: 1946-06-21
Abstract: 621,575. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd., EARP, C. W., and CLEAVER, R. F. June 21, 1946, No. 18736. [Class 40 (vii)] A radio system for determining the direction and distance of a co-operating mobile station from a fixed station, comprises means at said fixed station for radiating a first sinusoidallymodulated carrier wave, means at the mobile station for radiating a second carrier wave modulated in correspondence with the modulation of the first carrier wave as received at the mobile station, and means at the fixed station for automatically determining and jointly indicating the direction and distance of the mobile station from the second carrier wave received therefrom. The indication is preferably made by means of a polar co-ordinate type plan position indicator. At the fixed station a pulse generator 2 generates pulses of 8090 c/s which are applied to a divider circuit 3, the 809 c/s output wave from which is passed by filter 4 and applied to modulate transmitter 7 radiating on a frequency #1. At the mobile station, Fig. 2 (not shown), the received wave #1 is demodulated and the 809 c/s modulation passed through a filter and a phase-adjuster to correct for any variation in the modulationphase of the incoming and outgoing signals before being applied to modulate a transmitter radiating at a different frequency #2. The reradiated signals are received on direction-finding equipment 11 and 12, which may be similar to that described in Specification 490,940, and the output of which over lines 18 and 19 consists of two D.C. signals corresponding in sign and magnitude to the sine and cosine functions of the azimuth angle from which the wave #2 is received. These signals are applied to converter 20, which may be an arrangement such as described in Specification 590,260, [Group XXXVI], and the output from which is applied to the deflection system of a cathode-ray oscillograph 21 to repeatedly form a radial sweep trace 23, with an instantaneous fly-back, the direction of which corresponds to the direction from which the signals are received. The repetition frequency of the sweep is 809 c/s determined by pulse generator 22 connected to divider 3 and feeding controller 20. The modulation on the received signals is detected and applied through filter 24 and phase-adjuster 25, correcting for any phase changes in the apparatus, to pulse generator 26, the output pulses of which are used to modulate the intensity of the cathode-ray beam, so that a spot 28 appears on the trace. As phase variations in the apparatus have been corrected for, the position of spot 28 is dependent only on the distance to and from the mobile station and the spot represents the craft in range and bearing. As it is difficult to ensure that the scanning of the line 23 is strictly linear, a rangemarker may be provided by taking the 809 c/s output of filter 4 and passing it through a zero adjuster 30, calibrated variable-phase adjuster 31, to pulse generator 32 and the resulting pulses over switch 33 to form a bright spot rangemarker on the trace, adjustable to coincidence with the signal spot by phase-adjuster 31. In an alternative system, a scale is electronically marked on the trace by means of inverting the pulses from generator 2 at 34 and applying them over the other position of switch 33 to give a number of bright marking spots, the spacing between which represents one-tenth of the distance corresponding to the full cycle of the 809 c/s modulation, i.e. approximately 10 nautical miles. In order to differentiate between the signal spot and the marker spots the latter are arranged to be drawn out to small areas such as shown at 38 by means of an alternating magnetic field created by coil 35, round the tube, the coil being energized by oscillator 36 working at, say, 200 kc/s. The output of generator 22 is halved in frequency at 37 and the square waveform produced is applied to switch on for alternate traces the signindication or the marker indication(s); to prevent the signal spot also being drawn out oscillator 36 is blocked during the signal spot sweeps. Fig. 3 (not shown) indicates an alternative arrangement of the units within the dashed rectangle 1, in which the master oscillator of the system works at 809 c/s and a frequency multiplier is used to obtain the 8090 c/s pulses. By means of inputs 9 and 15 and switching means at the craft a two-way speech channel may be provided. Specification 579,117 also is referred to.